1. Field of the Invention
The present invention is directed to certain acetylene derivatives that are inhibitors of histone deacetylase and are therefore useful in the treatment of diseases associated with histone deacetylase activity. Pharmaceutical compositions and processes for preparing these compounds are also disclosed.
2. State of the Art
Interest in histone deacetylase enzymes (HDACs) as targets for pharmaceutical development has centered on the role of HDACs in regulating genes associated with cell-cycle progression and the development and progression of cancer (reviewed in Kramer et. al. Trends Endocrinol. Metab. 12, 294-300, (2001)). Several studies have shown that treatment of various cell lines with HDAC inhibitors leads to hyper acetylation of histone proteins and cell-cycle arrest in late G1 phase or at the G2/M transition. Genes involved in the cell cycle that have been shown to be up regulated by HDAC inhibitors include p21, p27, p53 and cyclin E. Cyclin A and cyclin D have been reported to be down regulated by HDAC inhibitors. In tumor cell lines, several studies have shown that treatment with HDAC inhibitors can lead to growth inhibition, growth arrest, terminal differentiation and/or apoptosis. In vivo studies have demonstrated growth inhibition of tumors and a reduction in tumor metastasis as a result of treatment with HDAC inhibitors.
The clearest link between abnormal HDAC activity and cancer occurs in acute promyelocytic leukemia. In this condition, a chromosomal translocation leads to the fusion of the retinoic acid receptor RARα with the promyelocytic leukemia (PML) or promyelocytic leukemia zinc-finger (PLZF) proteins. Both PML-RARα and PLZF-RARα promote the progression of leukemia by repressing retinoic acid-regulated genes through the abnormal recruitment of SMRT-mSin3-HDAC complex (Lin et. al. Nature 391, 811-814 (1998)); Grignani et al. Nature 391, 815-818 (1998)). Whereas the PML-RARα form of the disease is treatable with retinoic acid, the PLZF-RARα form is resistant to this treatment. For a patient with the retinoic acid-resistant form of the disease, the addition of the HDAC inhibitor sodium butyrate to the dosing regimen led to complete clinical and cytogenic remission (Warrell et al. J. Natl. Cancer. Inst. 90, 1621-1625, (1998)). HDACs have also been associated with Huntington's disease (Steffan, et al., Nature 413:739-744, “Histone deacetylase inhibitors arrest polyglutamine-dependent neurodegeneration in Drosophila”).
In summary, an increase in HDAC activity contributes to the pathology and/or symptomatology of a number of diseases. Accordingly, molecules that inhibit the activity of HDAC are useful as therapeutic agents in the treatment of such diseases.